1. Field of the Invention
The present invention relates to an electric power steering apparatus.
2. Description of the Related Art
An electric power steering apparatus is structured such that a pinion shaft connected to a steering shaft is engaged with a rack shaft. A worm gear is provided in a drive shaft connected to a steering assist motor. A worm wheel engaged with the worm gear is connected to the pinion shaft, whereby torque of a motor is transmitted to the rack shaft so as to assist steering operation.
In this case, on respective tooth faces of the worm gear and the worm wheel, a proper backlash is set in view of the particular requirement for working and operating. However, in the electric power steering apparatus, there is a case that the power transmitting direction is reversed due to operation of a steering wheel or vibration input from a road surface. In the reverse drive mentioned above, a tooth face at the back of the tooth face with which the worm gear or the worm wheel has been brought into contact suddenly moves at a degree of the backlash and collides with the opposing tooth face, whereby a striking sound is generated.
In the prior art as described in Japanese Patent Application Laid-Open Publication No. 11-171027, in order to reduce the striking sound as mentioned above, the structure is made such that a bush is provided in a bearing for supporting a drive shaft provided with a worm gear to a gear housing and an elastic body is interposed between the drive shaft and the bearing, whereby the drive shaft of the worm gear can be moved in an axial direction and an impact force generated on the tooth faces of the worm gear can be reduced by a bending deformation of the elastic body.
However, the structure of reducing the striking sound due to the reverse drive in the conventional electric power steering apparatus is made such that the bush is provided in the bearing and the elastic body is interposed between the drive shaft and the bearing. Therefore, the number of parts is increased and the number of steps for assembly is also increased.
An object of the present invention is to reduce the striking sound generated by a reverse drive by a simple structure in an electric power steering apparatus.
In accordance with the present invention, there is provided an electric power steering apparatus comprising:
a pinion shaft connected to a steering shaft being engaged with a rack shaft;
a bearing with an inner wheel and an outer wheel rotatably supporting a drive shaft connected to a steering assist motor, the drive shaft provided with a drive gear; and
an intermediate gear engaged with the drive gear, the intermediate gear being connected to the pinion shaft,
wherein the bearing of the drive shaft is connected to the drive shaft in an axial direction, and an elastic body is located between the inner and outer wheel. The elastic body elastically deforming at a load input time when respective tooth surfaces of the drive shaft and the intermediate gear are brought into contact with each other so as to move the drive shaft in an axial direction.